Molybdenum compounds have long been known as desirable lubricating oil additives for, among other things, friction reduction. Numerous molybdenum-containing compositions have been disclosed recently, including molybdenum-amine complexes, W. F. Marzluff, Inorg. Chem. 3, 345 (1964), molybdenum-oxazoline complexes, U.S. Pat. No. 4,176,074, Coupland, et al., and U.S. Pat. No. 4,176,073, Ryer, et al., molybdenum beta-keto esters, molybdenum diorganophosphates, U.S. Pat. No. 4,178,258, Papay, et al., etc.
A series of patents issued to King and De Vries and assigned to Chevron Research Company in 1981, disclosed lubricating oil compositions incorporating antioxidant molybdenum compounds, these patents being U.S. Pat. Nos. 4,259,194, 4,259,195, 4,261,843, 4,263,152, 4,265,773, 4,272,387, 4,283,295 and 4,285,822. The inventors state that the precise molecular formula of these molybdenum compounds is not known, but they are believed to be compounds with molybdenum oxides or sulfides complexed by or the salt of one or more nitrogen atoms from a basic nitrogen-containing composition (such as e.g., succinimide, carboxycyclic acid amide and Mannich bases) used to prepare the lubricant. U.S. Pat. No. 4,266,945, Karn, discloses a molybdenum-containing compound resulting from the reaction of a molybdenum acid (or salt thereof), a phenol or a condensation product of the phenol and a lower aldehyde, and a primary of secondary alkyl amine. U.S. Pat. No. 3,047,500, Matson, discloses what the patentees believe to be a molybdenum sulfide formed in situ as a result of the interaction of a molybdenum phenolate and an oil-soluble organic sulfur compound. These two ingredients are added to a lubricant for extreme pressure protection, there being no chemical interaction between the molybdenum and sulfur until substantial heat has been generated on the worked surfaces to produce the molybdenum sulfide. U.S. Pat. No. 4,202,781, Sabol, et al., a method of preparing a molybdenum phosphosulfurized hydrocarbon composition is disclosed, the composition being useful as an oxidation inhibitor and friction modifier for lubricants of internal combustion engines. The reaction disclosed products stable molybdenum-containing compositions without high temperatures, the use of ketone or ether-complexing solvents, or hydrogen peroxide.
The molybdenum compounds produced by the methods of the above-noted patents, all of which are expressly incorporated by reference herein, potentially suffer from either economic inefficiencies or from changing product requirements. For instance, at least one major U.S. automobile manufacturer has specified a maximum level of 0.11 percent phosphorus in motor oils used in internal combustion engines in 1983 and thereafter. Most commercially available oil-soluble molybdenum additives having anti-friction properties in lubricating oil contain phosphorus in the form of phosphosulfurized hydrocarbons or thiophosphates. However, the most effective antiwear additive commonly used in lubricating oils is a zinc-phosphorus composition, such as zinc dithiophosphate, which is useful in amounts to potentially account for the entire phosphorus "allotment" in lubricating oil. Therefore, a need exists for a molybdenum-containing additive which provides friction reduction properties at low cost without the use of phosphorus.
While the molybdenum compositions noted above can improve the characteristics of lubricating oils, they suffer the additional drawbacks that they are often uneconomical or difficult to prepare, cannot be prepared in a batch process, and may or may not have sufficient amounts of sulfur incorporated within the additive to benefit fully from the molybdenum contained therein. Accordingly, a need exists for an oil-soluble molybdenum composition which can be economically prepared, and which can provide high levels of activity to lubricating oils.